1. Field of the Invention
This invention relates to a control system for an automatic vehicle transmission.
2. Description of the Related Art
In the control of automatic transmissions, when power-on downshift (so-called xe2x80x9ckick-downxe2x80x9d; downshift with the accelerator pedal being depressed) occurs, the initial value of desired pressure to be supplied to the frictional engaging element such as a hydraulic clutch is usually determined by retrieving predetermined mapped data using a torque converter slip ratio, etc. as address data.
However, since it is quite difficult to identify the operating condition just before the power-on downshift occurs, the mapped data must have been prepared through experimentation taking every possible operating conditions into account. This requires much time and needs a great number of engineers to be involved. As a result, the volume of the mapped data becomes large, which necessitates a greater capacity of memory to be stored.
Moreover, since the initial value of the desired pressure is determined based on map-retrievable value obtained by the torque converter slip ratio, etc. in the prior art, it is difficult to follow the change in throttle opening satisfactorily and as a result, the shift shock may sometimes be increased.
An object of this invention is therefore to overcome the aforesaid problems and to provide a control system for automatic vehicle transmission, which determines the initial value of the desired pressure to be supplied to a frictional engaging element such as a hydraulic clutch appropriately so as to decrease the shift shock experienced by the vehicle occupant effectively, irrespectively of the change in he throttle opening, while ensuring to reduce the volume of the mapped data.
In order to achieve the objects, there is provided a system for controlling an automatic transmission of a vehicle having an input shaft connected to an internal combustion engine mounted on the vehicle and an output shaft connected to driven wheels of the vehicle, the transmission transmitting input torque, through any of frictional engaging elements, generated by the engine and inputted by the input shaft to the driven wheels by the output shaft, in accordance with predetermined shift scheduling defining a target gear based on detected operating conditions of the vehicle and the engine, comprising; operating condition detecting means for detecting the operating conditions of the vehicle and the engine including at least an engine speed; input shaft rotational speed detecting means for detecting an input shaft rotational speed inputted to the transmission; first torque calculating means for calculating an a first torque to be inputted to the transmission based on at least the detected operating conditions and the input shaft rotational speed; second torque calculating means for calculating a second torque necessary for advancing a torque necessary for advancing shifting in the transmission based on at least the detected operating conditions and the input shaft rotational speed, when the shifting is downshifting; desired value calculating means for calculating a desired value to be supplied to one of the frictional engaging element now being engaged based on a difference obtained by subtracting the second torque from the first torque; and hydraulic pressure control circuit for supplying hydraulic pressure to the one of the frictional engaging elements based on at least the calculated desired value.